1. Field of the Invention
This invention generally relates to an electronic device and a semiconductor device, and in particular, relates to an electronic device and a semiconductor device using a high frequency wave.
2. Description of the Related Art
Recently, radio wave such as a microwave or a milliwave (high frequency wave) is used in a communication field including a cellular phone. The high frequency wave is used for a radar or the like measuring a distance between two cars. A high-frequency-wave semiconductor device is often downsized, and is often mounted face down in order to restrain a loss of a signal. The high-frequency-wave semiconductor device is used for an electronic device using a high frequency wave.
The face-down mounting is a method of mounting a face, where a circuit portion using a high frequency wave is provided, on a wiring pattern of a package acting as a substrate mounted portion. Hereinafter, the face, where the circuit portion using the high frequency wave is provided, is referred to a front face and, a face backside of the front face is referred to a back face. The circuit portion is a circuit where an active device or a passive device are provided, the active device including such as a transistor or a diode, the passive device including such as a capacitor, a diode, or a wiring pattern. Or the circuit portion is a portion where a stand-alone device is provided.
In a high-frequency-wave semiconductor device, there are problems caused by a high frequency wave generated in the circuit portion. Japanese Patent Application Publication No. 9-102705 discloses an art (hereinafter referred to a conventional embodiment 1) where a dielectric substrate is provided in order to absorb an unnecessary electrical wave generated from a microwave integrated circuit mounted in a chassis, the dielectric substrate having a resistive layer on a face thereof facing to the microwave integrated circuit. Japanese Patent Application Publication No. 2005-217222 discloses an art (hereinafter referred to a conventional embodiment 2) where a shield layer is provided on a back face of an analog element mounted face down in order to limit a noise fed into the analog element, the shield layer being composed of a soft magnetic material.
In an electronic device having a high-frequency-wave semiconductor device, a high frequency wave generated in the circuit portion is reflected in a package and fed into the circuit portion as a reflection wave. In particular, a high frequency wave in a range 60 GHz to 80 GHz goes straight. And a reflection wave reflected in the package interferes a signal in the circuit portion. The high frequency wave from a circuit portion, which is provided on a substrate mounted face down, is reflected at a back face of the substrate. Thus, in a structure of the conventional embodiment 1, it is not possible to restrain that the high frequency wave emitted from the circuit portion is reflected at an interface between the substrate and the air and goes to the circuit portion. In a structure of the conventional embodiment 2, the high frequency wave is reflected at an interface between the substrate and the soft magnetic material. Thus, it is not sufficiently restrained that the high frequency wave emitted from the circuit portion is reflected and goes to the circuit portion. In addition, it is necessary to form a soft magnetic material of a few hundreds μm on a back face of the substrate. And the manufacturing cost increases.